R-270KM (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 10

R2

70WM

8 – 1

R269WM

Service Manual

 

1. CARRY OUT 3D CHECKS.

2. To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check across the magnetron filament leads should

indicate less than 1 ohm.

3. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads and chassis ground. This test should indicate

an infinite resistance. If there is little or no resistance the magnetron is grounded and must be replaced.

4. Reconnect all leads removed from components during testing.

5. Reinstall the outer case (cabinet).

6. Reconnect the power supply cord after the outer case is installed.

7. Run the oven and check all functions.

The following test procedure should be carried out with the microwave oven in a fully assembled condition (outer case fitted).

The power output of this oven is rated using the method specified by IEC 60705. Full details of how to curry out this procedure can be found in the
Sharp Technical Training notes which is available from Sharp Parts Centre (part number SERV-LITMW01).

The IEC60705 procedure must be carried out using laboratory-type procedures and equipment. 

These requirements make the procedure unsuitable for routine performance checks.

NOTE: The following test method gives an indication of the output power only, it cannot be used to establish the actual/rated output

Alternative simplified method:

1. Place 2 litres of cold water (between 12

°C and 20°C) in a suitable container.

2. Stir the water and measure the temperature in 

°C. Note temperature as T1.

3. Place the container in the microwave and heat the water for 1 minute and 48 seconds on full power.

NOTE: The operation time of microwave oven includes “3” sec. (3 sec. is magnetron filament heat-up time.)

4. When the 1 minute and 48 seconds is completed, remove the container and stir the water. Note the water temperature as T2.

5. Calculate the output power using the following formula:

R.F. Power Output = (T2 - T1) x 80.

NOTE: The result from this test should be within the allowance of 2000cc alternative method. (

±10%).

This oven should be tested for microwave leakage on completion of any repair or adjustment, following the procedure described in the Sharp Techni-
cal Training notes (part number SERV-LITMW01). The maximum leakage permitted in BS EN 60335-2-25 is 50W/m

2

 (equivalent to 5W/m

2

), however

it is not normal to detect any significant leakage, therefore, any leakage which is detected should be investigated.

It is essential that only leakage detectors with current calibration traceable to National Physical Laboratories are used.

Suitable leakage detectors: CELTEC A100

                                                 APOLLO X1

1. CARRY OUT 3D CHECKS.

2. Disconnect the leads to the primary winding of the high voltage transformer. Disconnect the filament and secondary winding connections from the

rest of the HV circuitry. Using an ohmmeter, set on a low range, it is possible to check the continuity of all three winding. The following readings
should be obtained:

                  a.Primary winding -------------------- 2.62 ohms approximately

                  b.Secondary winding --------------- 198.5ohms approximately 

                  c.Filament winding ------------------------------ less than 1 ohm

If the readings obtained are not stated as above, then the high voltage transformer is probably faulty and should be replaced.

WARNING: High voltages and large currents are present at the secondary winding and filament winding of the power transformer. It is